According to TweetStats, only 31.

7 of tweets originate from twitter.com, and those are the visitors that can be tracked back to tweets.Pugsley suggests testing this for yourself, by installing a twitter app like Tweetdeck, installing the Live HTTP headers plugin for Firefox, and clicking through the URL in a tweet, then looking at the referrer.His observation about missing Twitter traffic stats is not a new one, but probably still a topic that gets overlooked frequently.